PowerShell 5.1 Runspace中Write-Verbose无输出原因咨询

问题 #

我需要在PowerShell 5.1中实现多线程脚本，因此采用Runspace（而非ForEach-Object -Parallel）开发。但遇到问题：传递给AddScript方法的脚本块内，Write-Verbose的输出无法显示在脚本输出中，就算用-Verbose参数执行脚本，或者换成Write-Host/Write-Output也不行。

参考代码如下：

[runspacefactory]::CreateRunspacePool()
$SessionState = [System.Management.Automation.Runspaces.InitialSessionState]::CreateDefault()
$RunspacePool = [runspacefactory]::CreateRunspacePool(
    1, #Min Runspaces
    5 #Max Runspaces
)
$PowerShell = [powershell]::Create()
$PowerShell.RunspacePool = $RunspacePool
$RunspacePool.Open()

$Parameters = @{
    Param1 = 'Param1'
    Param2 = 'Param2'
}

$jobs = [System.Collections.ArrayList]::New()
1..10 | ForEach {
    $PowerShell = [powershell]::Create()
    $PowerShell.RunspacePool = $RunspacePool
    [void]$PowerShell.AddScript(
        {
            Param (
                $Param1,
                $Param2
            )

            $ThreadID = [appdomain]::GetCurrentThreadId()
            Write-Verbose "ThreadID: Beginning $ThreadID" -Verbose
            $Sleep = Get-Random (1..5)
            [PSCustomObject] @{
                Param1 = $Param1
                Param2 = $Param2
                Thread = $ThreadID
                ProcessID = $PID
                SleepTime = $Sleep
            }
            Start-Sleep -Seconds $Sleep
            Write-Verbose "ThreadID: Ending $ThreadID" -Verbose
        })
    [void]$PowerShell.AddParameters($Parameters)
    $Handle = $PowerShell.BeginInvoke()
    $temp = '' | Select PowerShell,Handle
    $temp.PowerShell = $PowerShell
    $temp.handle = $Handle
    [void]$jobs.Add($Temp)
    Write-Host ("Available Runspaces in RunspacePool: {0}" -f $RunspacePool.GetAvailableRunspaces())
    Write-Host ("Remaining Jobs: {0}" -f @($jobs | Where {
                                                $_.handle.iscompleted -ne 'Completed'
                                            }).Count)
}

# Verify completed
Write-Host ("Available Runspaces in RunspacePool: {0}" -f $RunspacePool.GetAvailableRunspaces())
Write-Host ("Remaining Jobs: {0}" -f @($jobs | Where {
                                            $_.handle.iscompleted -ne 'Completed'
                                        }).Count)

Write-Verbose "Waiting for jobs to finish..." -Verbose
$return = $jobs | ForEach {
    $_.powershell.EndInvoke($_.handle)
    $_.PowerShell.Dispose()
}
Write-Verbose "All jobs have finished" -Verbose

$jobs.Clear()

$return | Group ProcessID | Select Count, Name
$return | Group Thread | Select Count, Name
($return | Group Thread).Count

执行脚本后的输出示例：

C:\> .\parallel.ps1


InstanceId               : a965701a-f4d2-45d2-8200-f75fe77d6f72
IsDisposed               : False
RunspacePoolStateInfo    : System.Management.Automation.RunspacePoolStateInfo
InitialSessionState      :
ConnectionInfo           :
CleanupInterval          : 00:15:00
RunspacePoolAvailability : None
ThreadOptions            : Default
ApartmentState           : Unknown

Available Runspaces in RunspacePool: 4
Remaining Jobs: 1
Available Runspaces in RunspacePool: 3
Remaining Jobs: 2
Available Runspaces in RunspacePool: 2
Remaining Jobs: 3
Available Runspaces in RunspacePool: 1
Remaining Jobs: 4
Available Runspaces in RunspacePool: 0
Remaining Jobs: 5
Available Runspaces in RunspacePool: 0
Remaining Jobs: 6
Available Runspaces in RunspacePool: 0
Remaining Jobs: 7
Available Runspaces in RunspacePool: 0
Remaining Jobs: 8
Available Runspaces in RunspacePool: 0
Remaining Jobs: 9
Available Runspaces in RunspacePool: 0
Remaining Jobs: 10
Available Runspaces in RunspacePool: 0
Remaining Jobs: 10
VERBOSE: Waiting for jobs to finish...
VERBOSE: All jobs have finished
Count : 10
Name  : 5400

Count : 2
Name  : 14208

Count : 3
Name  : 7708

Count : 2
Name  : 13584

Count : 1
Name  : 1940

Count : 2
Name  : 17756

5

原因与解决方法 #

核心原因 #

Runspace中的脚本块运行在独立的执行上下文里，默认不会将流输出（Verbose、Host、Output等）转发到主控制台。另外：

• Write-Verbose依赖当前执行上下文的VerbosePreference设置，Runspace默认不会继承主会话的偏好设置；
• BeginInvoke()/EndInvoke()仅捕获脚本块的返回值（即示例中的[PSCustomObject]部分），不会捕获其他流的输出。

解决方法 #

要捕获并显示Runspace内的输出，需要为每个[powershell]实例设置输出流的重定向，同时继承主会话的偏好设置。

修改后的代码

# 初始化Runspace池
$RunspacePool = [runspacefactory]::CreateRunspacePool(1, 5)
$RunspacePool.Open()

$Parameters = @{
    Param1 = 'Param1'
    Param2 = 'Param2'
}

$jobs = [System.Collections.ArrayList]::New()
1..10 | ForEach {
    $psInstance = [powershell]::Create()
    $psInstance.RunspacePool = $RunspacePool
    
    # 传递主会话的Verbose状态
    $psInstance.AddParameter('Verbose', ($VerbosePreference -eq 'Continue')) | Out-Null
    
    [void]$psInstance.AddScript(
        {
            Param (
                $Param1,
                $Param2,
                [switch]$Verbose
            )

            # 显式设置当前上下文的Verbose偏好
            if ($Verbose) { $VerbosePreference = 'Continue' }

            $ThreadID = [appdomain]::GetCurrentThreadId()
            Write-Verbose "ThreadID: Beginning $ThreadID"
            $Sleep = Get-Random (1..5)
            $result = [PSCustomObject] @{
                Param1 = $Param1
                Param2 = $Param2
                Thread = $ThreadID
                ProcessID = $PID
                SleepTime = $Sleep
            }
            Start-Sleep -Seconds $Sleep
            Write-Verbose "ThreadID: Ending $ThreadID"
            
            return $result
        })
    [void]$psInstance.AddParameters($Parameters)
    
    # 监听Verbose流，实时输出到控制台
    $psInstance.Streams.Verbose.DataAdded += {
        param($sender, $e)
        $entry = $sender[$e.Index]
        Write-Host "VERBOSE: $($entry.Message)"
    }

    $Handle = $psInstance.BeginInvoke()
    $temp = '' | Select-Object PowerShell, Handle
    $temp.PowerShell = $psInstance
    $temp.Handle = $Handle
    [void]$jobs.Add($Temp)
    
    Write-Host ("Available Runspaces in RunspacePool: {0}" -f $RunspacePool.GetAvailableRunspaces())
    Write-Host ("Remaining Jobs: {0}" -f @($jobs | Where-Object { !$_.Handle.IsCompleted }).Count)
}

# 等待所有任务完成并处理结果
Write-Verbose "Waiting for jobs to finish..." -Verbose
$return = $jobs | ForEach-Object {
    $result = $_.PowerShell.EndInvoke($_.Handle)
    $_.PowerShell.Dispose()
    $result
}
Write-Verbose "All jobs have finished" -Verbose

$jobs.Clear()

$return | Group-Object ProcessID | Select-Object Count, Name
$return | Group-Object Thread | Select-Object Count, Name
($return | Group-Object Thread).Count

关键修改点 #

1. 继承Verbose偏好：将主会话的VerbosePreference状态传递给Runspace内的脚本块，显式设置上下文的输出偏好；
2. 实时捕获流输出：通过$psInstance.Streams.Verbose.DataAdded事件监听Verbose流，一旦有输出就实时转发到主控制台；
3. 分离实例变量：将循环内的$PowerShell变量改为$psInstance，避免变量覆盖导致的潜在问题。

内容的提问来源于stack exchange，提问作者James Bostock